In a process of performing biological analysis, biological samples and a reagent are placed in a test tube in order to extract the material to be analyzed. The concentration of the material that is extracted must be in an extent sufficient to be correctly analyzed. For example, when the DNA of a biological sample is to be extracted, normally, the biological sample is placed in a test tube, and subsequently the reagent for extracting the sample is added to mix therewith. In order to effectively extract the DNA, the reagent and the sample must be sufficiently mixed together, such that the concentration of the DNA can be high enough to be analyzed.
Conventionally, a plunger 100 is used for agitation in a test tube 20, vertically and reciprocally, (as shown in FIG. 1) to facilitate mixing the biological sample 102 with the reagent 104. A commonly used plunger is a solid cylinder or a tapered, solid cylinder. When in operation, to avoid the liquid in the test tube from spilling out as the plunger moves reciprocally in the test tube, a sufficiently large gap between the plunger and the test tube is maintained. However, if a gap is too large, the plunger agitation for mixing the sample and the reagent would be less effective.
Moreover, after the extraction process is completed, the extracted material must be drawn out of the test tube for subsequent analysis. Prior to drawing out the material, the plunger must be removed, and a suction pipette 30 is used (as shown in FIG. 2). However, at least two problems will arise during the removal of the plunger. First, the fluid adhered to the plunger may drip outside of the test tube. This not only increases the possibility of the operator's contact with the fluid, but will also contaminate the other test tubes if the fluid drips thereon and causes unanticipated hazardous results. Accordingly, such fluid dripping should be avoided when in the process of handling biological samples. Second, in an automatic process of handling the biological sample, the plunger is removed before the pipette is positioned into the test tube. In this situation, fluid can still drip onto the other test tubes and cause contamination, further complicating the operating process. Additional steps, such as grasping the tubes, removing the plungers, releasing the plungers, are also needed. These additional steps, however, decrease the efficiency of mixing the biological samples with the reagent.
In addition, since a biological sample is obtained by cutting off a chip or a small piece from organisms, the tissue of the sample can be broken into smaller pieces after they are agitated in the test tube. When a suction pipette is used, the sample chips or pieces will be drawn into the suction pipette and cause a blockage.
It is apparent from the above description that the plungers conventionally used still have some drawbacks that need to be overcome.